It is not uncommon to still find nits but no lice in the hair after treatment. Nits are easy to miss.

The nits (eggs) are attached to the hair shaft by a thick secretion the louse uses, almost like a super glue.  If her hair is fine and the comb is not doing the trick, you can also use your fingernails to pull them out. 

However, if your daughter’s school does NOT have a “no nit policy” you don’t necessarily have to remove all the nits.  If you used the Licefreee! treatment according to the directions, and the head and scalp was fully saturated in the product, any lice or nits in her hair should be dead.